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From: Yang Shi <yang.shi@linux.alibaba.com>
To: Andrew Morton <akpm@linux-foundation.org>,
	catalin.marinas@arm.com, hannes@cmpxchg.org, hdanton@sina.com,
	hughd@google.com, josef@toxicpanda.com,
	kirill.shutemov@linux.intel.com, linux-mm@kvack.org,
	mm-commits@vger.kernel.org, torvalds@linux-foundation.org,
	will.deacon@arm.com, willy@infradead.org, xuyu@linux.alibaba.com
Subject: Re: [patch 01/15] mm/memory.c: avoid access flag update TLB flush for retried page fault
Date: Thu, 23 Jul 2020 21:38:10 -0700
Message-ID: <30cf7356-bef1-c621-60cb-e12a8bd9111d@linux.alibaba.com> (raw)
In-Reply-To: <20200724041508.QlTbrHnfh%akpm@linux-foundation.org>



On 7/23/20 9:15 PM, Andrew Morton wrote:
> From: Yang Shi <yang.shi@linux.alibaba.com>
> Subject: mm/memory.c: avoid access flag update TLB flush for retried page fault
>
> Recently we found regression when running will_it_scale/page_fault3 test
> on ARM64.  Over 70% down for the multi processes cases and over 20% down
> for the multi threads cases.  It turns out the regression is caused by
> commit 89b15332af7c0312a41e50846819ca6613b58b4c ("mm: drop mmap_sem before
> calling balance_dirty_pages() in write fault").
>
> The test mmaps a memory size file then write to the mapping, this would
> make all memory dirty and trigger dirty pages throttle, that upstream
> commit would release mmap_sem then retry the page fault.  The retried page
> fault would see correct PTEs installed by the first try then update dirty
> bit and clear read-only bit and flush TLBs for ARM.  The regression is
> caused by the excessive TLB flush.  It is fine on x86 since x86 doesn't
> clear read-only bit so there is no need to flush TLB for this case.
>
> The page fault would be retried due to:
> 1. Waiting for page readahead
> 2. Waiting for page swapped in
> 3. Waiting for dirty pages throttling
>
> The first two cases don't have PTEs set up at all, so the retried page
> fault would install the PTEs, so they don't reach there.  But the #3 case
> usually has PTEs installed, the retried page fault would reach the dirty
> bit and read-only bit update.  But it seems not necessary to modify those
> bits again for #3 since they should be already set by the first page fault
> try.
>
> Of course the parallel page fault may set up PTEs, but we just need care
> about write fault.  If the parallel page fault setup a writable and dirty
> PTE then the retried fault doesn't need do anything extra.  If the
> parallel page fault setup a clean read-only PTE, the retried fault should
> just call do_wp_page() then return as the below code snippet shows:
>
> if (vmf->flags & FAULT_FLAG_WRITE) {
>          if (!pte_write(entry))
>              return do_wp_page(vmf);
> }
>
> With this fix the test result get back to normal.
>
> Link: http://lkml.kernel.org/r/1594148072-91273-1-git-send-email-yang.shi@linux.alibaba.com
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> Reported-by: Xu Yu <xuyu@linux.alibaba.com>
> Debugged-by: Xu Yu <xuyu@linux.alibaba.com>
> Tested-by: Xu Yu <xuyu@linux.alibaba.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Josef Bacik <josef@toxicpanda.com>
> Cc: Hillf Danton <hdanton@sina.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
>   mm/memory.c |    7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> --- a/mm/memory.c~mm-avoid-access-flag-update-tlb-flush-for-retried-page-fault
> +++ a/mm/memory.c
> @@ -4241,8 +4241,13 @@ static vm_fault_t handle_pte_fault(struc
>   	if (vmf->flags & FAULT_FLAG_WRITE) {
>   		if (!pte_write(entry))
>   			return do_wp_page(vmf);
> -		entry = pte_mkdirty(entry);
>   	}
> +
> +	if ((vmf->flags & FAULT_FLAG_WRITE) && !(vmf->flags & FAULT_FLAG_TRIED))
> +		entry = pte_mkdirty(entry);
> +	else if (vmf->flags & FAULT_FLAG_TRIED)
> +		goto unlock;

Hi Andrew,

It looks you forgot fold v2 update?

v2 is here 
https://lore.kernel.org/linux-mm/1594848990-55657-1-git-send-email-yang.shi@linux.alibaba.com/ 
and in -mm tree too.

> +
>   	entry = pte_mkyoung(entry);
>   	if (ptep_set_access_flags(vmf->vma, vmf->address, vmf->pte, entry,
>   				vmf->flags & FAULT_FLAG_WRITE)) {
> _



  reply index

Thread overview: 69+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-24  4:14 incoming Andrew Morton
2020-07-24  4:15 ` [patch 01/15] mm/memory.c: avoid access flag update TLB flush for retried page fault Andrew Morton
2020-07-24  4:38   ` Yang Shi [this message]
2020-07-24  4:56     ` Andrew Morton
2020-07-24 19:27   ` Linus Torvalds
2020-07-24 20:22     ` Linus Torvalds
2020-07-25  0:36       ` Yang Shi
2020-07-25  1:29         ` Linus Torvalds
2020-07-25 15:58           ` Catalin Marinas
2020-07-28  9:22             ` Will Deacon
2020-07-28  9:39               ` Catalin Marinas
2020-07-28 10:07                 ` Yu Xu
2020-07-28 11:46                   ` Catalin Marinas
2020-07-28 10:21                 ` Will Deacon
2020-07-28 18:28                 ` Linus Torvalds
2020-07-27 17:52           ` Yang Shi
2020-07-27 18:04             ` Linus Torvalds
2020-07-27 18:42               ` Catalin Marinas
2020-07-27 20:56                 ` Linus Torvalds
2020-07-27 22:34               ` Yang Shi
2020-07-27  7:31       ` Yu Xu
2020-07-27 11:05         ` Catalin Marinas
2020-07-27 17:01           ` Linus Torvalds
2020-07-28 11:19             ` Catalin Marinas
2020-07-27 17:12           ` Yu Xu
2020-07-27 18:04             ` Yang Shi
2020-07-27 18:37               ` Linus Torvalds
2020-07-27 22:43                 ` Yang Shi
2020-07-28  0:38                   ` Linus Torvalds
2020-07-28  0:13                 ` Yu Xu
2020-07-28 10:53                 ` Nicholas Piggin
2020-07-28 19:02                   ` Linus Torvalds
2020-07-28 22:53                     ` Nicholas Piggin
2020-07-29 13:58                       ` Michael Ellerman
2020-07-28  6:41             ` Yu Xu
2020-07-24  4:15 ` [patch 02/15] mm/mmap.c: close race between munmap() and expand_upwards()/downwards() Andrew Morton
2020-07-24  4:15 ` [patch 03/15] vfs/xattr: mm/shmem: kernfs: release simple xattr entry in a right way Andrew Morton
2020-07-24  4:15 ` [patch 04/15] mm: initialize return of vm_insert_pages Andrew Morton
2020-07-24  4:15 ` [patch 05/15] mm/memcontrol: fix OOPS inside mem_cgroup_get_nr_swap_pages() Andrew Morton
2020-07-24  4:15 ` [patch 06/15] mm/memcg: fix refcount error while moving and swapping Andrew Morton
2020-07-24 13:41   ` Alex Shi
2020-07-24  4:15 ` [patch 07/15] mm: memcg/slab: fix memory leak at non-root kmem_cache destroy Andrew Morton
2020-07-24  4:15 ` [patch 08/15] mm/hugetlb: avoid hardcoding while checking if cma is enabled Andrew Morton
2020-07-24  4:15 ` [patch 09/15] khugepaged: fix null-pointer dereference due to race Andrew Morton
2020-07-24  4:15 ` [patch 10/15] mailmap: add entry for Mike Rapoport Andrew Morton
2020-07-24  4:15 ` [patch 11/15] squashfs: fix length field overlap check in metadata reading Andrew Morton
2020-07-24  4:15 ` [patch 12/15] scripts/decode_stacktrace: strip basepath from all paths Andrew Morton
2020-07-24  4:15 ` [patch 13/15] io-mapping: indicate mapping failure Andrew Morton
2020-07-24  4:15 ` [patch 14/15] MAINTAINERS: add KCOV section Andrew Morton
2020-07-24  4:15 ` [patch 15/15] scripts/gdb: fix lx-symbols 'gdb.error' while loading modules Andrew Morton
2020-07-28  1:19 ` mmotm 2020-07-27-18-18 uploaded Andrew Morton
2020-07-28  2:14   ` Stephen Rothwell
2020-07-28  3:22   ` mmotm 2020-07-27-18-18 uploaded (drivers/scsi/ufs/: SCSI_UFS_EXYNOS) Randy Dunlap
2020-07-28  8:23     ` Alim Akhtar
2020-07-28 12:33   ` mmotm 2020-07-27-18-18 uploaded (mm/page_alloc.c) Randy Dunlap
2020-07-28 21:55     ` Andrew Morton
2020-07-28 22:20       ` Stephen Rothwell
2020-07-28 22:31         ` Andrew Morton
2020-07-29 14:18           ` Michael S. Tsirkin
2020-07-29 14:38             ` David Hildenbrand
2020-07-29 16:14               ` David Hildenbrand
2020-07-29 17:29                 ` Randy Dunlap
2020-07-28 22:39       ` Randy Dunlap
2020-07-29  1:43         ` Nathan Chancellor
2020-07-29  1:44         ` Andrew Morton
2020-07-29  2:04           ` Randy Dunlap
2020-07-29 14:09           ` make oldconfig (Re: mmotm 2020-07-27-18-18 uploaded (mm/page_alloc.c)) Alexey Dobriyan
2020-07-31 23:46 ` mmotm 2020-07-31-16-45 uploaded Andrew Morton
2020-08-01  5:24   ` mmotm 2020-07-31-16-45 uploaded (drivers/staging/vc04_services/) Randy Dunlap

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